The San Joaquin Valley: a geological history

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webmaster | 01/29/14
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We’re living in what once were three vast lakes

The San Joaquin Valley, the southern half of the large flat mountain-bound interior of California, has undergone many changes.

The Pacific Ocean birthed this valley we Maderans call home about 65 million years ago when it began to intermittently flood parts of the region. Eventually sediment from the sea and the rise of coastal mountain ranges choked off the valley from its mother 60 million years later.

Around 2 million years ago, glaciers started to transform the valley from a salty oceanic remnant into a freshwater lake. This was the Pleistocene Epoch, a time of ice ages, woolly mammoths, sabre-toothed cats, giant ground sloths, longhorned bison, birds with 25-foot wingspans, the first humans, and more. For a glimpse of the former locals, visit the Fossil Discovery Center of Madera County at 19450 Ave. 21 1/2 in Chowchilla.

The last of San Joaquin Valley’s great lakes would be Lake Corcoran, which filled much of the valley about 700,000 years ago. The lake drained into the Monterey Bay via the Salinas River. Then shifts in the earth’s crust lifted the valley and lowered the San Francisco Bay area. This threw part of the lake against the coastal mountains, and the brute force of rushing water, boulders, and other sediment gouged paths to the bay. To this day, those channels remain the deepest parts of the bay...

 

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